This report is part of the HyDelta 3 research program. The scope of Work Package WP1b.1 is to understand the impact of possible contamination within existing offshore natural gas networks on hydrogen purity and to define an approach for how to clean such pipelines. This work discusses the complete range of possible contamination of an upstream offshore natural gas pipeline. The key deliverable is a pipeline cleaning process that can be used to assess and clean an existing offshore natural gas pipeline and ensure that is it ready for hydrogen transport. The process is based on industry best practices for pigging pipelines combined with direct experience from of a small diameter onshore natural gas pipeline. Contact through Victoria.Monsma@dnv.com (not .nl as in the record) Dit project is medegefinancierd door TKI Nieuw Gas | Topsector Energie uit de PPS-toeslag onder referentienummer TKI2023-HyDelta.